The theory behind the popular blood-type diet is false, new research shows. Popularized in Peter D’Adamo’s book Eat Right for Your Type, the theory claims an individual’s nutritional needs vary by blood type. “Based on the data of 1,455 study participants, we found no evidence to support the ‘blood-type’ diet theory,” says Ahmed El-Sohemy, an associate professor and chair in nutrigenomics at the University of Toronto and senior author of the study published in PLOS ONE.